Various abbreviations that appear in the specification and/or in the drawing figures are defined as follows:    ACK acknowledgement    aGW access gateway    BCH broadcast channel    CCH control channel    CDM code division multiplexing    DL downlink    DTX discontinuous transmission    eNB EUTRAN Node B (evolved Node B)    EUTRAN evolved UTRAN    FDD frequency division duplex    FDMA frequency division multiple access    3GPP third generation partnership project    HARQ hybrid automatic repeat request    LTE long term evolution    NACK negative acknowledgement    Node B base station    OFDM orthogonal frequency domain multiplex    PDCCH physical downlink control channel    PHY physical (layer 1 or L1)    PS packet scheduler    RRC radio resource control (layer 2 or L2)    RV redundancy version    SCCH shared control channel    SC-FDMA single carrier, frequency division multiple access    SFN system frame number    TBS transport block set    TFI transport format indicator    TTI transmission time interval    UE user equipment    UL uplink    UTRAN universal terrestrial radio access network    VoIP voice over internet protocol
A proposed communication system known as evolved UTRAN (E-UTRAN, also referred to as UTRAN-LTE or as E-UTRA) is currently under development within the 3GPP. The current working assumption is that the DL access technique will be OFDMA, and the UL access technique will be SC-FDMA.
One specification of interest to these and other issues related to the invention is 3GPP TS 36.300, V8.2.0 (2007-09), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Access Network (E-UTRAN); Overall description; Stage 2 (Release 8), which is attached to the priority document as Exhibit A.
In wireless communication systems where control channel resources are limited, such as in LTE, it is desirable to provide optimizations to improve the utilization of the control channel resources. One optimization technique involves some type of persistent or semi-persistent allocation of transmission resources. This technique assigns the resources for transmission in the DL or UL for a longer period than one transmission (e.g., the resource(s) may be assigned for use by a UE for a number of time (transmission) periods. In the LTE system it has been agreed that semi-persistent scheduling will be used.
VoIP traffic is one type of traffic for which persistent or semi-persistent scheduling is desirable. Reference in this regard may be made to R2-070188, “Scheduling for VoIP”, Siemens Networks, 3GPP TSG RAN WG2#56bis, Sorrento, Italy, 15-19 Jan. 2007, which is attached to the priority document as Exhibit B. In general, persistent scheduling implies that a resource pattern is assigned to a UE for a relatively long period of time, without the need for continual scheduling grants over the L1/L2 control channel. With persistent scheduling, a VoIP UE is allowed to use the allocated physical resource blocks once every 20 ms, as depicted in FIG. 1.
Reduced signaling overhead and simplicity are the two main advantages for supporting persistent scheduling in LTE. Reference in this regard may be had to R2-070041, “Problems of Persistent Scheduling”, Ericsson, 3GPP TSG RAN WG2#56bis, Sorrento, Italy, 15-19 Jan. 2007, which is attached to the priority document as Exhibit C.
The main advantage of persistent scheduling is that DL or UL scheduling grants do not need to be transmitted for each VoIP frame, which reduces the control signaling overhead and thereby increases the system capacity. This is particularly beneficial as the L1/L2 control signaling resources are limited by the specification and in the case of VoIP (or other traffic characterized by periodically coming small packets with delay constraint) there is a need to schedule several user to the same TTI.
To reiterate, in that the periodicity pattern of transmission/reception resources are assigned to the UE with higher layer signaling (e.g., RRC signaling), then the UE can transmit or receive in those assigned resources without explicit L1/L2 control signaling (i.e., without the use of the PDCCH). One example is shown in FIG. 2, where a ‘talk spurt-based’ semi-persistent allocation is shown for a VoIP application. The RRC signaling is used to assign a 20 ms periodicity pattern to the UE. When traffic is identified in the beginning of the talk-spurt, the time and frequency resources and transport format are assigned to the UE with L1/L2 control signaling (i.e., with the PDCCH). The UE then stores an indication of these assigned time and frequency resources, and transport format information. This stored information informs the UE that it can either transmit (UL) or receive (DL) the assigned format of packets with these resources with the known periodicity pattern (signaled via RRC).
As shown in FIG. 2, re-transmissions in the DL are sent with L1/L2 control signaling, as the semi-persistent scheduling is typically applied for an initial (VoIP) packet transmission, even if it could be applied also for a first re-transmission of the packet.
DL asynchronous HARQ is specified in 3GPP for the LTE system, which means that for each TTI, in principle, a HARQ process can be assigned. The HARQ process number is informed to the UE via a DL allocation in the PDCCH. However, in semi-persistent scheduling the PDCCH is not used, and thus another problem that arises is how to inform the UE of which HARQ process is used for some certain semi-persistent allocation.
If only one HARQ process identification (ID) is used for the semi-persistent case then the problem would be more readily solved. However as can be seen from FIG. 2 that in this exemplary VoIP example only two re-transmissions would be possible until the same HARQ process is needed again for the semi-persistent transmission. This limitation has the potential to detrimentally affect the performance of the UE.
One possible solution would be to reserve more processes for semi-persistent use and/or to increase the number of HARQ processes. In both cases, however, there needs to be a mechanism in place to indicate which of the reserved HARQ processes are used in which semi-persistent transmission (without using PDCCH signaling). In one exemplary scenario the use of more HARQ processes can imply more signaling being required in the PDCCH, which in turn increases UE complexity and memory requirements. Alternatively, reserving more HARQ processes for semi-persistent scheduling, without increasing the total number of processes, would imply that the semi-persistently configured UE's other traffic throughput would suffer, as there would be fewer HARQ buffers available for the other traffic.
In co pending and commonly owned U.S. Provisional Patent Application No. 60/919,110, filed Mar. 19, 2007, “Apparatus, Method and Computer Program Product Providing Indication of Persistent Allocation on L1/L2 Control Channel” by Esa Malkamäiki (which is attached to the priority document as Exhibit D), the following is described. For asynchronous HARQ it is possible to reserve one (or several) HARQ process(es) for persistent allocation. The reservation can be performed, e.g., via RRC signaling. Thus, the HARQ process identification (ID) is descriptive of whether the allocation is a normal dynamic (one-time) allocation or is a persistent allocation to be stored and used for subsequent transmissions. The redundancy version (RV) or re-transmission sequence number (RSN) can be used to distinguish between an initial transmission (which is sent with L1 control only if the persistent allocation is changed) and re-transmission (e.g., RV=0/RSN=0 is reserved only for initial transmission). This shows one example how dynamic and semi-persistent allocations for initial or retransmissions can be distinguished from each other.
Other publications of interest to this invention include:    3GPP TS 36.321 V1.0.0 (2007-09) Technical Specification; 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) Medium Access Control (MAC) protocol specification (Release 8), attached to the priority document as Exhibit E;    3GPP TSG-RAN WG2 #55, R2-062788, Seoul (Korea), 9-13 Oct. 2006, NEC, “Persistent scheduling and dynamic allocation”, attached to the priority document as Exhibit F;    3GPP TSG-RAN WG2 Ad Hoc on LTE, R2-061920, Cannes, France, 27-30 Jun. 2006, NTT DoCoMo, Inc. “Persistent Scheduling”, attached to the priority document as Exhibit G;    3GPP TSG-RAN WG2 Ad Hoc on LTE, R2-061994, Cannes, France, 27-30 Jun. 2006, Motorola,. “R1-061734 Scheduling for Voice”, attached to the priority document as Exhibit H and;    3GPP TSG-RAN WG2 Meeting #57, R2-070475, St. Louis, USA, 12-16 Feb. 2007, Nokia, “Downlink Scheduling for VoIP”, attached to the priority document as Exhibit I;    3GPP TSG-RAN WG2 Meeting #57, R2-070476, St. Louis, USA, 12-16 Feb. 2007, Nokia, “Uplink Scheduling for VoIP”, attached to the priority document as Exhibit J;    3GPP TS 36.211 V8.0.0 (2007-09) Technical Specification; 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation (Release 8), attached to the priority document as Exhibit K; and    3GPP TS 36.212 V8.0.0 (2007-09) Technical Specification; 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding (Release 8), attached to the priority document as Exhibit L.